1. Field of the Invention
The present invention relates to an improved housing structure for fixedly holding a lens array for use in an optical reader or the like.
2. Description of the Related Art
In recent years, optical readers employ an element called a rod lens array. An example arrangement of such a rod lens array is disclosed in, for example, Japanese Patent Laid-Open Publication No. HEI-8-220645 entitled "STRUCTURE FOR FIXEDLY HOLDING A ROD LENS ARRAY FOR USE IN OPTICAL READER". The disclosed rod lens array comprises a plurality of columnar distributed index lenses made from a transparent material such as glass and plastics, arranged side by side in a row and then fixed by means of a resin. Thus, the array is elongate and has a rectangular cross section. In use, the array is held in a holder or a housing.
More specifically, the rod lens array is fitted in a U-shaped recess or groove formed in the holder and fixedly held therein by filling a space between a right wall defining part of the groove and a right wall of the lens array with a silicone resin and filling a space between a left wall of the groove and a left wall of the lens array with an acrylic resin.
Due to its flexibility, silicone resin is often used in this field of technology. However, it requires at least 30 minutes for the resin to become hardened. When complete hardening or setting needs to be assured, the resin should be allowed about 60 minutes to harden. During hardening of the resin, the rod lens array must be held immovably by means of an appropriate jig or clamp. This operation is tedious and time consuming, thereby making it difficult to achieve the desired increase in productivity.
To this end, there has been proposed as an adhesive a silicone-based resin which becomes hardened by ultraviolet rays in a shortened period of time. However, the proposed resin not only is expensive but also requires installations for producing unltraviolet rays, thereby increasing the cost of production of the end product.